INTRODUCTION: The most unwanted complication of tamoxifen is the development of endometrial carcinoma. In this study, we used transvaginal power Doppler ultrasound to determine endometrial vascular changes and compared them with the results of endometrial sampling. The diagnostic value of transvaginal power Doppler ultrasound was examined.METHODS: One hundred eleven breast cancer patients were included in the study. Endometrial, uterine, adnexal, and vascular evaluations were performed. Endometrial sampling was recommended to patients whose endometrial thickness was over 5 mm and was done in 73 patients.RESULTS: Group 1 (n=62) consisted of patients receiving tamoxifen and group 2 (n=49) consisted of patients who were not using tamoxifen. There were four endometrial polyps (5.5%) in the sample results in Group 2. Twenty patients (14 tamoxifen using and 6 non-tamoxifen using) had abnormal vascular changes on power Doppler examination but none of them had any malignant changes. There were abnormal vascular patterns on power Doppler examination in all of the patients detected with endometrial polyps. Three of them had benign measurable Doppler flow characteristics while one of them had non-measureable flows. All of the patients detected to have an endometrial polyp were pre-menopausal and did not use tamoxifen.DISCUSSION AND CONCLUSION: Transvaginal power Doppler ultrasound is an effective method for determining vascular changes in the endometrium. However, it is not enough for defining the lesion accurately in breast cancer patients. Moreover, it is not useful in determining which patients require invasive intervention.